Not for nothing, and I am speaking of experience(CDL A with School Bus endorsement for 20 years), but if they(the volunteer FD & EMS) want this to be as realistic as possible, the crash should involve the school bus and a much larger vehicle instead of the one used.
Reason: School buses are manufactured under strict state and federal regulations regarding design, and materials used in construction of school buses. Basically they are a shell within a shell for the protection of the passengers. The small car used in this training exercise, wouldn't even cause a blister on a passenger let alone trap anyone on the bus.
A more realistic training model would be using a vehicle roughly the same size as the school bus as that would cause severe damage to the bus as well as cause serious injuries to the passengers and the possibility of extrication measure being needed.